The electric current that a battery produces is the result of an electrochemical, oxidation-reduction reaction. Generally, this reaction is exothermic, i.e., it produces thermal energy or heat as well as an electric potential between the battery's electrodes. Heat in a battery is also produced as a result of current flowing in the electrodes and terminals.
It is important that a battery be stored and operated within a temperature range prescribed for the particular battery chemistry. The reaction rate in a battery depends upon, among other things, temperature. Generally, the higher the temperature of the reactants, the faster the reaction will proceed. A battery stored or operated at high temperatures will have reduced storage or operating lifetimes. Further, a battery operated in a high temperature environment will have a lower voltage across its terminals than one operated within the prescribed temperature range. In addition, a battery operated at temperatures below the prescribed temperature range will produce less current and reach a state of discharge more quickly than a battery operated in the specified temperature environment. Not only is it important that a battery be stored and operated within the prescribed temperature range, it is also important to maintain the battery within the recommended temperatures when recharging the battery.
Accordingly, there is a need for methods and apparatus for transferring thermal energy to and from a battery to maintain the temperature of the battery within a temperature range prescribed for the particular battery chemistry during storage, use, and recharging operations.